Micro-porous mesh stent with hybrid structure

ABSTRACT

A prosthesis for treating a body passage includes a micro-porous tubular element and a support element. The tubular element is formed from a thin-walled sheet having a wall thickness of 25 micrometers or less, preferably a coiled-sheet exhibiting temperature-activated shape memory properties. The mesh pattern includes a plurality of openings in the sheet having a maximum dimension of not more than about 200 micrometers, thereby acting as a filter trapping embolic material while facilitating endothelial growth therethrough. The support element includes a plurality of struts, preferably having a thickness of 100-150 micrometers. The support element is preferably an independent component from the tubular element. Alternatively, the support element may be attached to or integrally formed as part of the tubular element. The tubular and support elements are placed on a catheter in contracted conditions and advanced endoluminally to a treatment location within a body passage. The tubular element is deployed, and the support element is expanded to an enlarged condition at the treatment location to engage an interior surface of the tubular element, thereby securing the tubular element and holding the lumen of the treatment location open.

FIELD OF THE INVENTION

The present invention relates generally to endoluminal prostheses or“stents,” and more particularly to stents including a micro-porous meshstructure supported by an integral or separate strut structure, and tomethods of making and deploying such stents.

BACKGROUND

Tubular prostheses or “stents” are often implanted within blood vessels,for example, within the coronary and carotid arteries, for treatingatherosclerotic disease that may involve one or more stenoses. Stentsgenerally have a tubular shape capable of assuming a radially contractedcondition to facilitate introduction into a patient's vasculature, andan enlarged condition for engaging the vessel wall at a treatmentlocation.

Plastically deformable stents have been suggested that are initiallyprovided in their contracted condition, and placed over a balloon on anangioplasty catheter. At the treatment location, the balloon is inflatedto plastically deform the stent until it is expanded to its enlargedcondition.

Self-expanding stents have also been suggested that are biased to assumean enlarged condition but may be radially compressed to a contractedcondition. The stent may be mounted to a delivery device and constrainedin the contracted condition during delivery, for example, by anoverlying sheath. At the treatment location, the stent may be released,for example, by retracting the sheath, the stent automatically resumingits enlarged condition to engage the vessel wall.

In addition to tubular stents, coiled-sheet stents have been suggestedthat include a flat sheet rolled into a spiral or helical shape havingoverlapping inner and outer longitudinal sections. Such stents generallyhave a lattice-like structure formed in the sheet and a plurality offingers or teeth along the inner longitudinal section for engagingopenings in the lattice. Once deployed at a treatment location, thefingers may engage openings in the lattice to lock the stent in theenlarged condition.

One of the problems with many stent structures, whetherballoon-expandable or self-expanding, is that they substantially exposethe underlying wall of the treatment location. For example, helical wirestent structures generally have substantial gaps between adjacent turnsof the wire. Multi-cellular stent structures, which may include a seriesof slotted or zig-zag-shaped cells, create large spaces within and/orbetween the cells, particularly as they expand to their enlargedcondition. The lattice structure of coiled-sheet stents generally alsoincludes relatively large openings.

Thus, despite holding the wall of the treatment location generally open,the openings or gaps in these stents may substantially expose thebloodstream to plaque, tissue prolapse, or other embolic materialattached to the wall of the vessel. This embolic material may beinadvertently released during or after deployment of the stent, and thentravel downstream where it may cause substantial harm, particularly ifit reaches a patient's neurovasculature.

One proposed solution to address the issue of embolic containment is tocover a conventional stent with a fabric or polymer-type material. Thissolution has met with limited success, however, because of thepropensity to form false lumens due to poor apposition of the coveringand the vessel wall.

Accordingly, it is believed that a stent capable of supporting the wallof a blood vessel being treated, while substantially minimizing exposureof embolic material to the bloodstream, would be considered useful.

SUMMARY OF THE INVENTION

The present invention is directed to an endoluminal prosthesis or“stent” including a micro-porous mesh structure and a support structure,and to methods of making and implanting such stents. In accordance withone aspect of the present invention, a micro-porous mesh structure forsupporting a wall of a body passage is provided that includes agenerally tubular body having a contracted condition for facilitatingdelivery into the body passage, and an enlarged condition for engagingthe wall of the body passage, the tubular body having a preferred wallthickness of not more than about 25 micrometers (0.001 inch). Aplurality of openings are provided in the tubular body defining a meshpattern therein, each opening preferably having a maximum dimension ofnot more than about 200 micrometers (0.008 inch).

In a preferred form, the tubular body is a coiled-sheet havingoverlapping inner and outer sections formed from a material, such asNitinol, exhibiting temperature-activated shape memory properties. Aplurality of struts may be formed integrally onto the tubular body andspaced along a length of the tubular body for supporting the tubularbody against the wall of the body passage, having, for example, athickness of about 100-150 micrometers (0.004-0.006 inch).

In accordance with another aspect of the present invention, a prosthesisfor supporting a wall of a body passage is provided that includes atubular element, such as the micro-porous mesh structure describedabove, and a separate support element including a plurality of strutsfor engaging an interior surface of the tubular element. The supportelement is preferably biased to an enlarged condition at bodytemperature for substantially securing the tubular element against thewall of the body passage in the enlarged condition. The support elementmay be any of a variety of known stent structures, such as acoiled-sheet stent, preferably formed from a material, such as Nitinol,exhibiting temperature-activated shape memory properties.

In accordance with yet another aspect of the present invention, a methodfor making a prosthesis for supporting a wall of a body passage includesproviding a sheet formed from a shape memory alloy, preferably having atransition temperature between a substantially ambient temperature andbody temperature, the sheet having a wall thickness of not more thanabout 25 micrometers (0.001 inch). A mesh pattern is formed in the sheetthat includes a plurality of micro-porous openings, and the sheet isformed into a generally tubular body, for example, by rolling it into acoiled-sheet having overlapping inner and outer sections.

The tubular body may be heat treated at a first temperaturesubstantially higher than the transition temperature to program anexpanded condition for engaging the wall of the body passage into theshape memory material. The tubular body may then be cooled to a secondtemperature below the transition temperature, and compressed into acontracted condition for facilitating delivery into the body passage.

In one preferred form, the sheet has an initial wall thickness greaterthan about 25 micrometers (0.001 inch) and not more than about 150micrometers (0.006 inch). Portions of the sheet are removed to provide aplurality of struts having a thickness similar to the initial wallthickness separating thin-walled regions having a final wall thicknessof not more than about 25 micrometers (0.001 inch). In another preferredform, a separate strut element may be provided for supporting thetubular body that may be attached to the tubular body.

In accordance with still another aspect of the present invention, amethod for supporting a wall of a predetermined location within a bodypassage incorporates a prosthesis including a micro-porous tubularelement and a separate support element, such as that described above.The tubular and support elements are placed in contracted conditions ona distal region of a delivery device, such as a catheter. The distalregion of the delivery device is advanced endoluminally within the bodypassage to the predetermined location. The tubular element is deployedat the predetermined location, and the support element is expanded to anenlarged condition to engage an interior surface of the tubular element,thereby substantially securing the tubular element against the wall ofthe predetermined location.

Preferably, the support element is biased to expand to its enlargedcondition at body temperature such that upon deployment from thedelivery device, the support element automatically expands to engage theinterior surface of the tubular element. The tubular element may beexpanded to an enlarged condition as the support element expands to itsenlarged condition, or alternatively, the tubular element may also bebiased to expand to an enlarged condition at body temperature such thatthe tubular element automatically expands to its enlarged condition toconform to the wall of the predetermined location upon deployment fromthe delivery device.

Thus, a prosthesis in accordance with the present invention may be usedto treat a stenosis within a blood vessel, such as within the carotid,coronary or cerebral arteries. The tubular element may substantiallytrap embolic material against the wall of the vessel once secured by thesupport element, while the micro-porous mesh pattern facilitatesendothelial growth, thereby substantially reducing the risk of releasingembolic material into the bloodstream. Also, the provision of amicro-porous mesh structure and a separate support structure may allowthe support structure to slide along the surface of the tubular elementwithout significantly disturbing the underlying diseased vessel wall.

In addition, in a preferred embodiment, the micro-porous mesh structureis biased to its enlarged condition such that the tubular body may tendto expand out to engage the vessel wall. Thus, the micro-porous meshstructure may contact the vessel wall at points between the struts ofthe support structure, thereby minimizing the creation of false lumensor other gaps between the micro-porous mesh structure and the vesselwall.

Other objects and features of the present invention will become apparentfrom consideration of the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first preferred embodiment of atwo-stage stent in accordance with the present invention, including amicro-porous tubular element and a support element.

FIG. 2A is a detail of the wall of the tubular element of FIG. 1,showing a first preferred form of a micro-porous mesh pattern therein.

FIG. 2B is a detail of the wall of FIG. 2A, with the openings partiallycompressed.

FIG. 3 is a cross-sectional view of a second preferred embodiment of astent including a micro-porous tubular element with an integral supportelement.

FIG. 4A is a cross-sectional view of a distal region of a deliverydevice with a stent in accordance with the present invention mountedthereon.

FIGS. 4B-4D are cross-sectional views, showing the delivery device andstent of FIG. 4A being directed to a treatment location within a bodypassage where the stent is implanted.

FIG. 5 is a cross-sectional view of a bifurcation between main andbranch vessels across which a third preferred embodiment of a stent inaccordance with the present invention is implanted.

FIG. 6 is a perspective view of a third preferred embodiment of atwo-stage stent in accordance with the present invention, including amicro-porous tubular element and a support element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, FIG. 1 shows a first preferred embodimentof a stent 10 in accordance with the present invention. Generally, thestent 10 includes two elements, namely a micro-porous tubular element 12and a support element 14. Both elements 12, 14 have a contractedcondition for facilitating introduction into a body passage, such as apatient's vasculature, and an enlarged condition for engaging the wallof a treatment location, such as a stenotic region of a blood vessel.

The micro-porous tubular element 12 is preferably formed from a shapememory alloy, such as Nitinol, having a plurality of openings 16defining a micro-porous mesh pattern therein. The mesh pattern is“micro-porous” in that the openings 16 are sufficiently small such thatthey substantially prevent plaque or other embolic material fromextending through the openings 16. Thus, the tubular element 12 maybehave as a filter, allowing endothelial growth to occur through theopenings 16 while substantially protecting the patient from the releaseof embolic material through the mesh pattern. Openings 16 having amaximum open dimension of not more than about 400 micrometers (0.016inch) are preferred to provide an effective micro-porous mesh pattern,with openings between about 80 micrometers (0.003 inch) and about 200micrometers (0.008 inch) being more preferred.

Turning to FIG. 2A, in a preferred form, the mesh pattern includes astaggered pattern of substantially circular openings 16 in the shapememory alloy material. The openings 16 are preferably spaced apart fromone another such that the resulting tubular element 12 has a surfacecoverage of not more than about 20 percent, i.e., not more than about 20percent of the overall surface area of the vessel wall covered by thetubular element 12 is directly engaged with stent material. Thisrelatively low percentage of remaining stent material after formation ofthe mesh pattern may enhance the flexibility of the tubular element 12,thereby facilitating its conformance with the wall of a treatmentlocation, as well as facilitating delivery through tortuous anatomy.Alternatively, other opening shapes may be provided, such as diamonds,triangles, rectangles, or ovals. An important feature of the openings 16is that they are not likely to over-expand when the tubular element 12is expanded to its enlarged condition, which may otherwise increase therisk of embolic material being exposed or escaping through them.

Returning to FIG. 1, the tubular element 12 preferably has acoiled-sheet configuration. The tubular element 12 is formed from a flatsheet (not shown), preferably having a wall thickness of not more thanabout 25 micrometers (0.001 inch). The plurality of openings 16 areformed in the flat sheet, for example, by laser drilling, etching orother known processes. The openings 16 may be arranged substantiallyuniformly along the length of the flat sheet, or alternatively, thespacing, shape and/or size of the openings 16 may be varied in apredetermined manner along the length of the flat sheet to createdesired properties in the finished tubular element 12, e.g., a desiredtransverse flexibility, expansion bias, compressibility, etc. thatvaries along the length of the resulting tubular element 12.

The flat sheet is then rolled into a coiled-sheet having overlappinginner and outer sections 22, 24. In one preferred form, the inner andouter sections 22, 24 define a longitudinal seam 26 between them thatextends substantially parallel to a longitudinal axis 28 of the tubularelement 12. Alternatively, the inner and outer sections may beoverlapped such that they define a helical seam between them thatextends down a length of the tubular element 12, as shown in FIG. 6. Inthe latter alternative, the flat sheet may have a generallyparallelogram shape rather than a rectangular shape.

Preferably, the sheet is formed from a nickel-titanium alloy(“Nitinol”), or other shape memory alloy, and more preferably from amaterial exhibiting temperature-activated shape memory properties. Forexample, the material may have a transition temperature betweensubstantially ambient temperatures and body temperature. Thus, atsubstantially ambient temperatures, for example, below about 25 degreesCelsius, the material may be substantially martensitic, while at bodytemperature, for example, at or above 37 degrees Celsius, the materialmay be substantially austenitic.

The coiled-sheet may be formed into a desired size and shape, preferablyinto a desired enlarged condition for engaging a predetermined sizedlumen of a blood vessel. For example, the coiled-sheet may be formedinto a generally cylindrical shape having a diameter of between about 2mm and about 14 mm, depending upon the size of the target lumen. Thecoiled-sheet may then be heat treated at temperatures substantiallyhigher than body temperature, for example, at a temperature of about 600degrees Celsius or higher, for a predetermined time to program the sizeand shape into the material's shape memory.

The coiled-sheet may then be cooled below its transition temperature,for example, to a temperature of about zero degrees Celsius or less. Atthis temperature, the coiled-sheet is preferably radially compressed toits contracted condition, i.e., compressed in-plane, and also coiled, toachieve dense packing. Compressing the coiled-sheet in-plane involveselastically deforming the sheet itself, i.e., compressing thecoiled-sheet material about its longitudinal axis, thereby compressingthe plurality of openings 16 defining the mesh pattern, as shown in FIG.2B. In the contracted condition, the openings 16 may thus be partiallyclosed in a direction about the circumference of the coiled-sheet. Afterpacking, the coiled-sheet may be compressed by about three hundredpercent or more, i.e., the circumferential dimension of the coiled-sheetin the contracted condition may be about one third or less than in theenlarged condition. The sheet is also preferably coiled further,possibly creating multiple overlapping sections. When the coiled-sheetis coiled in this manner, it may retain its contracted condition, or itmay remain biased to at least partially unwind.

The coiled-sheet may then be placed on a delivery device, such as acatheter having an overlying sheath or other constraint, as describedmore particularly below. When the delivery device is introduced into apatient's vasculature, the coiled-sheet becomes exposed to bodytemperature, i.e., to a temperature above its transition temperature,causing the material to return to its austenitic phase. This activatesthe Nitinol material's shape memory, biasing the coiled-sheet towardsits enlarged condition. When deployed from the delivery device, thecoiled-sheet may at least partially expand towards the enlargedcondition, preferably to substantially conform to the wall of the vesselat the deployment site.

Although the tubular element 12 is preferably self-supporting, becauseof the relatively thin wall thickness of the sheet, the tubular element12 may not be sufficiently strong to support the diseased vessel. Forthis reason, the inner longitudinal edge 18 of the coiled-sheetgenerally may not include teeth or fingers, as provided on conventionalcoiled-sheet stents. The primary purpose of the tubular element 12 is toconform to and substantially cover the wall of the vessel at a treatmentlocation and trap any embolic material between the tubular element 12and the wall of the vessel. Locking fingers and the like may interferewith this conformability and/or with the ability of the coiled-sheet tounroll during deployment, as may irregularly shaped openings in the meshpattern. Therefore, it is generally preferred that the coiled-sheet havea substantially smooth wall, thereby enhancing the unrolling of thecoiled-sheet and its conformance with an irregular vessel wall.

Returning to FIG. 1, the support element 14 generally providesstructural support for holding the tubular element 12 against the vesselwall and holding the lumen of the vessel open. The support element 14includes a plurality of struts 30 spaced apart along the longitudinalaxis 28 for engaging an interior surface 32 of the tubular element 12.The struts 30 preferably have a thickness of between about 100micrometers (0.004 inch) and about 150 micrometers (0.006 inch). In afirst preferred form, the support element 14 is biased to its enlargedcondition at body temperature, similar to the temperature-activatedshape memory material described above for the tubular element 12, suchthat the support element 14 may substantially secure the tubular element12 against the wall of a vessel in its enlarged condition, as describedfurther below. Alternatively, the support element 14 may be plasticallydeformable from its contracted condition to its enlarged condition.

The structure of the support element 14 may take a variety of forms.Known and/or commercially available stents may be appropriate for use asa support element for the micro-porous tubular element 12 describedabove. For example, the support element 14 may be a coiled-sheet stenthaving a lattice structure (not shown), such as those disclosed in U.S.Pat. No. 5,443,500 issued to Sigwart, or U.S. Pat. No. 5,007,926 issuedto Derbyshire, the disclosures of which are expressly incorporatedherein by reference. Alternatively, the support element 14 may be ahelical wire stent, such as those disclosed in U.S. Pat. No. 4,665,918issued to Garza et al. or U.S. Pat. No. 4,553,545 issued to Maass etal., a wire mesh stent, such as those disclosed in U.S. Pat. No.5,871,538 issued to Dereume or U.S. Pat No. 5,221,261 issued to Terminet al., a multi-cellular slotted stent, such as those disclosed in U.S.Pat. Nos. 4,733,665 or 4,739,762 issued to Palmaz, or a zig-zag stent,such as those disclosed in U.S. Pat. No. 4,580,568 issued to Gianturco,or U.S. Pat. No. 5,843,120 issued to Israel et al. The disclosure ofthese patents and any others referenced therein are expresslyincorporated herein by reference. Other known stent structures (notshown) may also be used which, for example, substantially engage theinterior of the tubular body 12 and provide sufficient support for thewall of the body passage.

In one form, the support element 14 may be attached directly to thetubular element 12. For example, the struts 30 of the support element 14may be substantially permanently attached continuously or at discretelocations where they contact the interior surface 32 of the tubularelement 12, e.g., using an adhesive or by welding. Thus, the tubularelement 12 and support element 14 may be provided as a single unit thatis mounted on a delivery device and deployed together at a treatmentlocation.

More preferably, the support element 14 is provided separate from thetubular element 12, and the two elements 12, 14 are deployedindependently from one another. Thus, the stent 10 may be deployed in atwo-stage method for supporting a wall of a predetermined location, suchas a stenosis, within a blood vessel or other body passage, for example,within the renal, iliac, femoral arteries, and preferably within thecarotid, cerebral or coronary arteries. In addition, the stent 10 may beimplanted within a degenerated bypass graft within one of thesearteries.

Initially, as shown in FIG. 4A, the tubular and support elements 12, 14are placed in their contracted conditions on a distal region of adelivery device 49. The delivery device 40 preferably includes acatheter 42 having a proximal end (not shown) and a distal end 44 havinga size and shape for facilitating introduction into a patient'svasculature. The delivery device 40 also preferably includes a tubularsheath 46 that may be advanced over the distal end 44 of the catheter 42to constrain the tubular and support elements 12, 14 in their contractedconditions. In a preferred form, the tubular element 12 is placedconcentrically over the support element 14 on the distal end 44 of thecatheter 42. Alternatively, the tubular element 12 and the supportelement 14 may be placed adjacent one another on the distal end of thecatheter (not shown).

In addition to or instead of the sheath 46, other constraints (notshown) may be associated with the delivery device 40 for securing thetubular and support elements 12, 14 axially on the distal end 44 of thecatheter 42 and/or for preventing premature expansion of the tubular andsupport elements 12, 14 from their contracted conditions. For example,one or more wire elements (not shown) may be extended through lumens(also not shown) in the catheter 42 from the proximal end that may bedetachably connected to the tubular or support elements 12, 14. The wireelements may be woven through apertures (not shown) in the tubular orsupport elements 12, 14 and subsequently withdrawn at time ofdeployment, similar to those shown and described in U.S. Pat. No.5,824,053 issued to Khosravi et al., the disclosure of which isexpressly incorporated herein by reference.

The distal end 44 of the catheter 42 may then be percutaneouslyintroduced into a peripheral vessel of a patient (not shown), such asthe femoral artery, and advanced endoluminally through the patient'svasculature to a predetermined treatment location, such as a stenotic oroccluded region 50 within a blood vessel 52, as shown in FIG. 4B. Anangioplasty, atherectomy or other similar procedure may have beenpreviously performed at the treatment location 50 to open the treatmentlocation 50 or otherwise prepare the location 50 for implantation of thestent 10.

As shown in FIG. 4C, the tubular element 12 may be placed across thetreatment location 50 and deployed, for example, by withdrawing thesheath 46 or other constraints securing it to the delivery device 40.Preferably, the tubular element 12 is self-expanding, i.e., is biased toexpand towards its enlarged condition, for example, by providing thetubular element 12 from a shape memory material, such as thetemperature-activated Nitinol previously described. Thus, when thetubular element 12 is released from the delivery device 40, itautomatically expands to its enlarged condition to conform substantiallyto the size and shape of the wall of the treatment location 50.Alternatively, the tubular element 12 may only partially expand or mayrequire a balloon or other expandable member on the catheter or aseparate device (not shown) to expand it to its enlarged condition.

The support element 14 may be released simultaneously with the tubularelement 12, e.g., when the sheath is withdrawn from the distal end 44 ofthe catheter 42. Alternatively, the delivery device 40 may includeadditional constraints (not shown) that may secure the support element14 independently of the tubular element 12 to allow successivedeployment of the support and tubular elements 12, 14. The supportelement 14 is also preferably self-expanding, i.e., is biased to expandto substantially engage the wall of the treatment location 50 and holdthe lumen of the vessel 52 substantially open. Thus, when the supportelement 14 is released from the catheter 42, it may automatically expandto its enlarged condition to engage the interior surface 32 of thetubular element 12, thereby substantially securing the tubular element12 against the wall of the vessel 50 at the treatment location 50 andholding the lumen of the vessel 52 substantially open, as shown in FIG.4D.

Where the tubular and support elements 12, 14 are both self-expandingand simultaneously deployed, the tubular element 12 may be biased toexpand more rapidly than the support element 12, thereby ensuring thatthe tubular element 12 conforms to the size and/or shape of thetreatment location 50 before being substantially secured by the supportelement 14 against the wall thereof. Where the support element 14 isself-expanding and the tubular element 12 is not, the tubular element 12may be expanded to its enlarged condition as the support element 14 isdeployed and automatically expands to its enlarged condition. Stateddifferently, the support element 14 may provide sufficient radiallyoutward force to expand the tubular element 12, for example, to cause acoiled-sheet tubular element 12 to unroll and conform to thecross-section of the vessel 52.

Once deployed, the support element 14 substantially secures the tubularelement 12 against the wall of the vessel 52 and preferably providessufficient radial support to hold the lumen of the vessel 52substantially open. The tubular element 12 substantially traps anyembolic material attached to the wall of the treatment location 52against the wall of the vessel 50. Thus, the patient may besubstantially protected from the release of embolic material during orafter deployment that might otherwise travel downstream and potentiallycause substantial harm, particularly within the arteries leading to thebrain. Because of the micro-porous mesh pattern, however, the stent 10continues to allow endothelial growth through the tubular element 12.

Generally, friction may sufficiently maintain the relative position ofthe tubular and support elements 12, 14 within the vessel. Morepreferably, the support element 14 may slidably engage the interiorsurface 32 of the tubular element 12, thereby accommodating some naturaladjustment of the stent 10 after deployment. Alternatively, the supportelement 14 may be attached to the tubular element 12 during deployment,for example, using an adhesive on the interior surface 32 of the tubularelement 12 or the support element 14.

Turning to FIG. 3, a second preferred embodiment of a hybrid stent 110is shown that includes a support element 114 that is integrally formedwith a tubular element 112. Generally, the tubular element 112 issimilar to the separate tubular element 12 described above. Instead of aseparate support element 14, however, a plurality of struts 130 may beformed directly from the sheet material of the tubular element 112. Thestruts 130 may simply be annular shaped members that extendsubstantially around the circumference of the tubular element 112, or amore complicated strut design (not shown) may be formed to providepredetermined structural properties, such as enhanced transverseflexibility, as will be appreciated by those skilled in the art. Thestruts 130 may extend from an interior surface 132 of the tubularelement 112, as shown, may extend from an exterior surface (not shown),or alternatively may be formed along either or both of the interior andexterior surfaces.

In a preferred method for making the hybrid stent 110, a flat sheet,preferably formed from a shape memory material, such as thetemperature-activated Nitinol described above, is provided having apredetermined initial thickness. In a preferred form, the initialthickness of the flat sheet is the desired thickness of the strutsdefining the support element 114. For example, a flat sheet having athickness of between about 100 micrometers (0.004 inch) and about 150micrometers (0.006 inch) may be provided.

Material is then selectively removed from a surface of the flat sheet,for example, using an etching process, to thin predetermined regions 134of the flat sheet, preferably to a desired thickness of the tubularelement 112, e.g., not more than about 25 micrometers (0.001 inch).Thus, after the removal process, a plurality of struts 130 remain havinga thickness similar to the initial wall thickness that separaterelatively thin-walled regions 134 defining the tubular element 112. Amesh pattern (not shown) may be formed in the thin-walled regions 134,and then the flat sheet may be formed into a coiled-sheet and/or heattreated, similar to the previously described embodiment.

The stent 110 may then be placed on a delivery device, similar to thecatheter and sheath described above, delivered into a patient's bodypassages, and implanted at a predetermined treatment location, similarto the methods described above.

Turning to FIG. 5, another preferred embodiment of a multiple-stagestent 210 in accordance with the present invention is shown that may beimplanted across a bifurcation between a main vessel 250 and a branchvessel 252, such as the common carotid artery (CCA), the internalcarotid artery (ICA), and the external carotid artery (ECA) . The stent210 generally includes a pair of micro-porous tubular elements 212 a,212 b and a single support element 214, similar to the embodimentsdescribed above.

To implant the stent 210, the tubular elements 212 a, 212 b may beplaced on a distal portion of a delivery device, such as a cathetersimilar to that described above (not shown). Preferably, the tubularelements 212 a, 212 b are spaced apart axially from one another on thedistal portion by a predetermined distance, such as a distancecorresponding substantially to the size of the branch vessel 252, e.g.at least about 5 mm and more preferably 10 mm or more. Alternatively,the tubular elements 212 a, 212 b may be mounted adjacent one anotherand successively deployed at a treatment location. A sheath and/or otherconstraints (not shown) may be used to secure the tubular elements 212a, 212 b on the delivery device.

The support element 214 may be provided on the delivery device under thetubular elements 212 a, 212 b, similar to the embodiments describedabove. Alternatively, the support element 214 may be mounted on thedelivery device proximate the tubular elements 212 a, 212 b tofacilitate successive delivery of the tubular and support elements 212,214. In a further alternative, the support element 214 may be mounted ona separate delivery device.

With the tubular and support elements 212, 214 thereon, the distalportion of the delivery device may be percutaneously introduced into aperipheral vessel and advanced into the main vessel 250 until thetubular elements 212 a, 212 b straddle the branch vessel 252. Thetubular elements 212 a, 212 b may then be deployed, for example, bywithdrawing the overlying sheath, the tubular elements 212 a, 212 bpreferably automatically expanding to conform to the wall of the mainvessel 250 on either side of the branch vessel 252. Alternatively, thedistal tubular element 212 a may be positioned and deployed first distal(e.g. downstream) of the bifurcation, and then the proximal tubularelement 212 b may be positioned and deployed proximal (e.g. upstream) ofthe bifurcation. The catheter and/or tubular elements 212 a, 212 b mayinclude radiopaque markers and the like, allowing a physician toexternally visualize the tubular elements 212 a, 212 b, for example,using fluoroscopy, to position the tubular elements 212 a, 212 brelative to the bifurcation before deployment.

The support element 214 may be deployed simultaneously with the tubularelements 212 a, 212 b or may be separately constrained on the deliverydevice and deployed subsequent to the tubular elements 212 a, 212 b. Ifseparately deployed, the support element 214 may be positioned withinthe main vessel 250 until the support element 214 spans the branchvessel 252 with respective end regions 216 a, 216 b of the supportelement being located within the interior of the tubular elements 212 a,212 b. The support element 214 may be expanded to substantially engagethe tubular elements 212 a, 212 b and hold the lumen of the main vessel250 open.

The length of the support element 214 preferably correspondssubstantially to the length of the tubular elements 212 a, 212 b and thespace between them. For example, if tubular elements 212 a, 212 b havinga length of about 15 mm are to be implanted that are spaced apart fromone another by about 10 mm, the support element 214 should have a lengthof about 40 mm.

Once implanted, the stent 210 substantially supports the lumen of themain vessel 250, the tubular elements 212 a, 212 b substantiallytrapping embolic material against the wall of the main vessel 250. Thespace between the tubular elements 212 a, 212 b allows substantiallyunobstructed blood flow through the branch vessel 252, because of therelatively large openings, i.e., open-celled structure, in the supportelement 214. In an alternative method, the stent 210 may be implanted toextend from the main blood vessel 250 into the branch vessel 252 (notshown) in a similar method to that described, as will be appreciated bythose skilled in the art.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims.

What is claimed is:
 1. A micro-porous mesh structure for supporting awall of a body passage, comprising: a generally tubular body having acontracted condition for facilitating delivery into the body passage,and an enlarged condition for engaging the wall of the body passage, thetubular body being biased to its enlarged condition; a plurality ofstruts formed integrally onto the tubular body and spaced along a lengthof the tubular body for supporting the tubular body against the wall ofthe body passage, the struts separating relatively thin-walled regionstherebetween; and a plurality of openings in the relatively thin-walledregions of the tubular body defining a micro-porous mesh patterntherein; wherein the tubular body comprises a coiled-sheet havingoverlapping inner and outer sections.
 2. The micro-porous mesh structureof claim 1, wherein each opening has a maximum dimension of not morethan about 400 micrometers (0.016 inch).
 3. The micro-porous meshstructure of claim 1, wherein the tubular body has a wall thickness ofnot more than about 25 micrometers (0.001 inch).
 4. The micro-porousmesh structure of claim 1, wherein the inner and outer sections define ahelical seam therebetween that extends down a length of the tubularbody.
 5. The micro-porous mesh structure of claim 1, wherein the innerand outer sections define a longitudinal seam therebetween that extendssubstantially parallel to a longitudinal axis of the tubular body. 6.The micro-porous mesh structure of claim 1, wherein the plurality ofstruts have a thickness of between about 100 micrometers (0.004 inch)and about 150 micrometers (0.006 inch).
 7. The micro-porous meshstructure of claim 1, wherein the plurality of openings are spaced apartfrom one another on a surface of the tubular body such that remainingtubular body material provides not more than about 20 percent coverageof the wall of the body passage.
 8. A micro-porous mesh structure forsupporting a wall of a body passage, comprising: a generally tubularbody having a contracted condition for facilitating delivery into thebody passage, and an enlarged condition for engaging the wall of thebody passage, the tubular body being biased to its enlarged condition; aplurality of struts formed integrally onto the tubular body and spacedalong a length of the tubular body for supporting the tubular bodyagainst the wall of the body passage, the struts separating relativelythin-walled regions therebetween; and a plurality of openings in therelatively thin-walled regions of the tubular body defining amicro-porous mesh pattern therein; wherein the tubular body comprises ashape memory alloy.
 9. The micro-porous mesh structure of claim 8,wherein the shape memory alloy is plastically deformable at or belowsubstantially ambient temperatures to facilitate compressing the tubularbody into its contracted condition.
 10. The micro-porous mesh structureof claim 9, wherein the plurality of openings are at least partiallycompressed when the body is placed in its contracted condition.
 11. Themicro-porous mesh structure of claim 9, wherein the shape memory alloyhas a transition temperature between substantially ambient temperaturesand body temperature, whereby the tubular body is biased to the enlargedcondition when exposed to body temperature.
 12. The micro-porous meshstructure of claim 11, wherein the plurality of openings are biased toreturn to a fully open condition when exposed to body temperature.
 13. Aprosthesis for supporting a wall of a body passage, comprising: asubstantially flexible, conformable tubular element defining a lengthand a circumference and having a plurality of openings defining amicro-porous mesh pattern therein, the tubular element having acontracted condition for facilitating delivery into the body passage,and an enlarged condition for engaging the wall of the body passage; anda support element comprising a plurality of struts for engaging aninterior surface of the tubular element, the support structure beingexpandable between a contracted condition and an enlarged condition forsupporting the tubular element; wherein the support element is biased tothe enlarged condition at body temperature for substantially securingthe tubular element against the wall of the body passage.
 14. Theprosthesis of claim 13, wherein the plurality of openings each have amaximum dimension of not more than about 400 micrometers (0.016 inch).15. The prosthesis of claim wherein the support element comprises ashape memory alloy.
 16. The prosthesis of claim 15, wherein the shapememory alloy comprises Nitinol having a transition temperature between asubstantially ambient temperature and body temperature.
 17. Theprosthesis of claim 13, wherein the support element is attachable to thetubular element during deployment.
 18. The prosthesis of claim 13,wherein the support element is substantially permanently attached to theinterior surface of the tubular element.
 19. The prosthesis of claim 13,wherein the support element has a wall thickness of not more than about150 micrometers (0.006 inch).
 20. The prosthesis of claim 13, whereinthe tubular element has a wall thickness of not more than about 25micrometers (0.001 inch).
 21. The prosthesis of claim 13, wherein thetubular element has a substantially smooth wall and side edges.
 22. Aprosthesis for supporting a wall of a body passage, comprising: asubstantially flexible, conformable tubular element defining a lengthand a circumference and having a plurality of openings defining amicro-porous mesh pattern therein, the tubular element having acontracted condition for facilitating delivery into the body passage,and an enlarged condition for engaging the wall of the body passage; anda support element comprising a plurality of struts for engaging aninterior surface of the tubular element, the support structure beingexpandable between a contracted condition and an enlarged condition forsupporting the tubular element; wherein the support element comprises acoiled-sheet stent.
 23. A prosthesis for supporting a wall of a bodypassage, comprising: a substantially flexible, conformable tubularelement defining a length and a circumference and having a plurality ofopenings defining a micro-porous mesh pattern therein, the tubularelement having a contracted condition for facilitating delivery into thebody passage, and an enlarged condition for engaging the wall of thebody passage; and a support element comprising a plurality of struts forengaging an interior surface of the tubular element, the supportstructure being expandable between a contracted condition and anenlarged condition for supporting the tubular element; wherein thesupport element slidably engages the tubular element in the enlargedcondition.
 24. A prosthesis for supporting a wall of a body passage,comprising: a substantially flexible, conformable tubular elementdefining a length and a circumference and having a plurality of openingsdefining a micro-porous mesh pattern therein, the tubular element havinga contracted condition for facilitating delivery into the body passage,and an enlarged condition for engaging the wall of the body passage; anda support element comprising a plurality of struts for engaging aninterior surface of the tubular element, the support structure beingexpandable between a contracted condition and an enlarged condition forsupporting the tubular element; wherein the tubular element comprises acoiled-sheet having overlapping inner and outer sections.
 25. Aprosthesis for supporting a wall of a body passage, comprising: asubstantially flexible, conformable tubular element defining a lengthand a circumference and having a plurality of openings defining amicro-porous mesh pattern therein, the tubular element having acontracted condition for facilitating delivery into the body passage,and an enlarged condition for engaging the wall of the body passage; anda support element comprising a plurality of struts for engaging aninterior surface of the tubular element, the support structure beingexpandable between a contracted condition and an enlarged condition forsupporting the tubular element; wherein the tubular element comprises ashape memory alloy.
 26. The prosthesis of claim 25, wherein the shapememory alloy has a transition temperature between substantially ambienttemperatures and body temperature, whereby the tubular element is biasedto its enlarged condition when exposed to body temperature.
 27. A methodfor making a prosthesis for supporting a wall of a body passage, themethod comprising the steps of: providing a sheet formed from a shapememory alloy having an initial wall thickness; removing portions of thesheet to provide a plurality of struts having a thickness similar to theinitial wall thickness; forming a mesh pattern comprising a plurality ofmicro-porous openings in relatively thin-walled regions between thestruts; and forming the sheet into a generally tubular body.
 28. Themethod of claim 27, wherein each opening has a maximum dimension of notmore than about 200 micrometers (0.008 inch).
 29. The method of claim27, wherein the sheet has a wall thickness of not more than about 25micrometers (0.001 inch).
 30. The method of claim 27, wherein the meshpattern is formed by chemically etching, laser cutting, punching, ordrilling the micro-porous openings through the sheet.
 31. The method ofclaims 27, wherein the step of forming the sheet into a generallytubular body comprises rolling the sheet into a coiled-sheet havingoverlapping inner and outer sections.
 32. The method of claim 27,wherein the shape memory alloy has a transition temperature between asubstantially ambient temperature and body temperature, and wherein themethod comprises the additional steps of: heat treating the tubular bodyat a first temperature substantially higher than the transitiontemperature to program an expanded condition for engaging the wall ofthe body passage into the shape memory material; cooling the tubularbody to a second temperature below the transition temperature; andcompressing the tubular body at the second temperature into a contractedcondition for facilitating delivery into the body passage.
 33. A methodfor supporting a wall of a predetermined location within a body passageusing a prosthesis comprising a substantially flexible, conformabletubular element including a micro-porous mesh pattern therein, and asupport element, the method comprising the steps of: providing thetubular and support elements in contracted conditions on a distal regionof a delivery device, the tubular element and the support element beingplaced adjacent one another on the distal region of the delivery device;advancing the distal region of the delivery device endoluminally withinthe body passage to the predetermined location; deploying the tubularelement at the predetermined location such that the tubular elementsubstantially conforms to the wall of the predetermined location;directing the support element across the predetermined location afterthe tubular element is deployed; and expanding the support element to anenlarged condition at the predetermined location to engage an interiorsurface of the tubular element, thereby substantially securing thetubular element against the wall of the predetermined location.
 34. Amethod for supporting a wall of a predetermined location within a bodypassage using a prosthesis comprising a substantially flexible,conformable tubular element including a micro-porous mesh patterntherein, and a support element, the method comprising the steps of:providing the tubular and support elements in contracted conditions on adistal region of a delivery device, the delivery device comprising oneor more constraints for preventing the tubular and support elements fromexpanding from their contracted conditions after the tubular and supportelements are placed on the distal region of the delivery device;advancing the distal region of the delivery device endoluminally withinthe body passage to the predetermined location; deploying the tubularelement at the predetermined location such that the tubular elementsubstantially conforms to the wall of the predetermined location; andexpanding the support element to an enlarged condition at thepredetermined location to engage an interior surface of the tubularelement, thereby substantially securing the tubular element against thewall of the predetermined location; wherein the support element isbiased to expand to its enlarged condition at body temperature, andwherein the step of expanding the support element comprises releasingthe support element from at least one of the constraints, the supportelement automatically expanding to engage the interior surface of thetubular element.
 35. The method of claim 34, wherein at least one of theconstraints comprises a sheath overlying at least one of the tubular andsupport elements.
 36. The method of claim 34, wherein the tubularelement is deployed at the treatment location by releasing it from atleast one of the constraints.
 37. The method of claim 34, wherein thetubular element is expanded to an enlarged condition as the supportelement expands to its enlarged condition, the tubular element therebyconforming substantially to the shape of the body passage.
 38. Themethod of claim 34, wherein the tubular element is biased to expand toan enlarged condition at body temperature, and wherein the step ofdeploying the tubular element comprises releasing the tubular elementfrom at least one of the constraints, the tubular element automaticallyexpanding to its enlarged condition to conform to the wall of thepredetermined location.
 39. The method of claim 38, wherein the tubularelement is mounted concentrically over the support element on the distalregion of the delivery device, and wherein the tubular and supportelements are released simultaneously from the constraints, the tubularelement expanding more rapidly than the support element to conform tothe cross-section of the predetermined location before beingsubstantially secured by the support element against the wall thereof.40. The method of claim 34, wherein the predetermined location comprisesa stenotic region.
 41. The method of claim 34, wherein the body passagecomprises a carotid artery, a coronary artery, or a cerebral artery. 42.A method for treating a bifurcation between a main blood vessel and abranch blood vessel using a prosthesis comprising first and secondsubstantially flexible, conformable micro-porous tubular elements, andan open-celled support element, the method comprising the steps of:advancing the first and second tubular elements and the support elementin a contracted condition endoluminally into the main blood vessel;deploying the first tubular element in one of the main and branch bloodvessel distally of the bifuircation such that the first tubular elementsubstantially conforms to the wall of the respective blood vessel; anddeploying the second tubular element in the main blood vessel proximallyof the bifurcation such that the second tubular element substantiallyconforms to the wall of the main blood vessel; and expanding the supportelement to an enlarged condition across the bifurcation to engage aninterior surface of each of the first and second tubular elements,thereby substantially securing the first and second tubular elementsagainst the wall of their respective blood vessels.
 43. The method ofclaim 42, wherein the first and second tubular elements are mounted to adistal portion of a delivery device in contracted conditions, andwherein the advancing step comprises advancing the distal portion withthe first and second tubular elements in their contracted conditionsinto the main blood vessel.
 44. The method of claim 43, wherein thefirst and second tubular elements are spaced apart from one another onthe distal portion by a distance corresponding substantially to a widthof the bifurcation.
 45. The method of claim 42, wherein the supportelement is mounted to the distal portion of the delivery device in itscontracted condition before being advanced into the main blood vessel.46. The method of claim 45, wherein the delivery device comprises asheath overlying the first and second tubular elements, and wherein thesteps of deploying the first and second tubular elements comprisessuccessively withdrawing the sheath from over the first and secondtubular elements.
 47. The method of claim 46, wherein the supportelement is mounted on the distal portion underneath the first and secondtubular elements, and wherein the support element is deployed from thedelivery device as the sheath is withdrawn from over the first andsecond tubular elements.
 48. The method of claims wherein the supportelement is biased to its enlarged condition at body temperature suchthat the support element automatically expands to the enlarged conditionas it is deployed from the delivery device.
 49. The method of claim 42,wherein the first and second tubular elements are biased to an enlargedcondition for conforming to the wall of a blood vessel such that thefirst and second tubular elements automatically expand to their enlargedconditions during the deploying steps to conform substantially to thewall of the respective blood vessels.